Coal

Overview
Coal is an abundant ore in Survival 303, having the most locations out of any ore in the entire game. It is on a total of 12 islands, surpassing even Iron Ore with 10.

It is mainly used for crafting Steel Mix or Charcoal, which are both extremely important resources for mid-game and end-game.

Despite being so common, it still makes for a decent trading resource for tribes that live on Mainland and other islands without coal.